Air filter



FIG. 1 is a perspective view of an air filter in the present design;

FIG. 2 is a front view of an air filter in the present design;(a rear view being the same),

FIG. 3 is a left view of an air filter in the present design;(a right view being the same);

FIG. 4 is a top view of an air filter in the present design; and,

FIG. 5 is a bottom view of an air filter in the present design. 

The ornamental design for an air filter, as shown and described. 